Power converter device for one of several motor windings on reluctance motor

ABSTRACT

A power converter device for a switched reluctance motor, comprises a semiconductor circuit arrangement in the form of an asymmetric inverter (T 1 , D 1 ; T 2 , D 2 ), to supply one of the motor windings ( 4, 6 ) on the reluctance motor with current or to commutate the current from the winding. According to the invention, the achievement of the maximum possible current amplitude may be accelerated and the commutating of the current from the motor winding ( 4, 6 ) may be accelerated, whereby, in addition to the main voltage source (U d ), an additional voltage source in the form of a circuit extension (SE) is provided, which, by means of providing an additional voltage of corresponding polarity, accelerates the current feed to the relevant motor winding ( 4, 6 ), or accelerates the removal of the current (commutating) from the motor winding.

[0001] The invention relates to a power converter apparatus for one oftwo or more motor windings in a switched reluctance motor.

[0002] A power converter apparatus such as this has a semiconductorcircuit arrangement in the form of an asymmetric inverter, which is fedfrom a m voltage source, in particular a DC voltage intermediatecircuit.

[0003] First of all, a known power converter apparatus for a switchedreluctance motor will be described with reference to FIGS. 1 and 2.

[0004] As is shown in FIG. 1, a reluctance motor 1 contains a rotor 2which has at least three poles and with which at least two stator partsS1 and S2 are associated. The stator part S1 comprises a motor winding 4and a core 8, while the stator part S2 comprises a motor winding 6 and acore 10. The motor windings 4 and 6 are connected to power converterapparatuses 12 and 14, respectively, which are both fed from a voltageU_(d), which is produced by a main voltage source which in this case isin the form of a DC voltage intermediate circuit 20. A control device 16controls both the power converter apparatuses 12 and 14.

[0005]FIG. 2 shows a 30own power converter apparatus 12 or 14, connectedto an associated respective motor winding 4 or 6.

[0006] The power converter apparatus contains two series circuits, eachformed by a respective power semiconductor T1 or T2, and a diode D1 orD2.

[0007] The connecting nodes N1 and N2 between the respective powersemiconductors and the diodes form the connections between therespective power converter apparatus and the associated motor winding.

[0008] As is known with a reluctance motor such as this, the gradient ofthe inductance change increases as the motor speed increases, for whichreason the desired current amplitude is no longer reached at high motorspeeds, at which the time which is available for current to flow to andfrom the motor winding becomes ever shorter. This reduces the drivingtorque. Furthermore, the decay in the current is delayed. If the decayduration of the current is too great, this results in a braking torque.

[0009] The invention is based on the object of specifying a powerconverter apparatus of the type mentioned initially, by means of which atorque which is considerably better than that with known apparatuses isachieved, in particular at relatively high motor speeds.

[0010] According to the invention, this object is achieved in that anadditional voltage source with a variable polarity is connected inseries with the motor winding (the motor phase), and in that a controldevice is provided, which, matched to the operation of the inverter,

[0011] a) provides an additional positive driving voltage from theadditional voltage source when current is flowing through the motorwinding; and/or

[0012] b) assists the off-commutation of the current from the motorwinding by means of an additional negative voltage from the additionalvoltage source, and

[0013] c) when required, can make the additional voltage sourceinoperative.

[0014] The basic idea of the invention is to speed up the current flowto the motor winding by increasing the voltage, in order that thedesired current amplitude can be reached more quickly, and/or to speedup the drop in voltage during the off-commutation process, by using anegative voltage.

[0015] The additional voltage source preferably produces avariable-amplitude voltage. The variable amplitude of the additionalvoltage allows the operation of the reluctance motor to be optimallymatched to the respective requirements.

[0016] It is particularly advantageous for the additional voltage sourceto be formed by an energy store which is fed from the connected motorwinding. The additional voltage source preferably then comprises acapacitor, which is connected in series with the motor phase and withthe main voltage source by means of drivable semiconductor switches. Thedirect connection of the additional voltage source to the motor windingprevents the rest of the inverter circuit, which corresponds to theknown power converter apparatus, from being subjected to an increasedvoltage and current load.

[0017] The capacitor, which acts as an energy store, is connectedtogether with drivable semiconductor switches to the motor winding. Thedrivable semiconductor switches are operated by the control device onthe basis of the requirements for the respective operating state. Apartfrom this drive for the semiconductor switches for the connectedcapacitor, no further measures are required. This means that theadditional voltage source according to the invention together with theassociated elements can be designed as an autonomous circuit extension,which can also be retrofitted and which can be connected withoutproblems to existing power converter apparatuses, for example also inthe form of a plug connection.

[0018] Owing to the autonomous character of the circuit extensionaccording to the invention, it can be connected or disconnected asrequired. This option offers numerous advantages for practical use, aswill be described in more detail further below.

[0019] One preferred embodiment of the power converter apparatusaccording to the invention provides the following features:

[0020] a) the semiconductor switch arrangement of the asymmetricinverter comprises two branches, and each branch has in each case oneswitchable power semiconductor, for example a power transistor, which isconnected in series with a diode which is reverse-biased with respect tothe DC voltage intermediate circuit, with the diode in one branch beingconnected to the negative pole of the DC voltage intermediate circuit,and that in the other branch being connected to the positive pole of theDC intermediate circuit;

[0021] b) the motor winding and the circuit extension according to theinvention, comprising a capacitor, two diodes and two switchable powersemiconductors, are connected in series between the connecting nodes ofthe elements of the two series circuits; and

[0022] c) the capacitor is connected by means of semiconductor switchessuch that energy is drawn from it, energy is stored in it, or the stateof charge on the capacitor is not changed.

[0023] In particular, the invention provides for two series circuitseach comprising a diode and a semiconductor switch to be connected inparallel with the capacitor, whose connecting nodes are connected to theconnecting nodes of one of the two series circuits of the asymmetricinverter, and to the motor winding. These elements of the powerconverter circuit according to the invention or of the circuit extensionfor a power converter circuit may in a relatively simple manner be inthe form of a module which can be connected or plugged in.

[0024] Various operating modes can now be provided, depending on thedrive to the semiconductor switches, for the asymmetric inverter and forthe semiconductor switches which are associated with the capacitor.

[0025] One particularly important operating mode provides for bothsemiconductor switches in the circuit extension to be open during theoff-commutation of the current from the motor winding. The current thenflows via the two diodes, which are connected to the plates of thecapacitor, so that the capacitor is charged with an appropriatepolarity.

[0026] The power semiconductors (transistors) in the two branches(series circuits), which are connected in parallel, of the asymmetricinverter can then be driven in a different operating mode. The variantin which both power semiconductors are closed is of secondaryimportance.

[0027] In a first preferred operating mode, provision is made for thetwo power semiconductors of the asymmetric inverter to be open. Thiscorresponds to “hard” commutation. The current is carried exclusivelyvia the diodes of the two circuits, which are connected in parallel withone another, of the asymmetric inverter, both the voltage from the mainvoltage source and the increasing voltage from the additional voltagesource ensuring that the phase current decreases very rapidly. A voltagewhose value is dependent on the capacitance of the capacitor, thecurrent flow duration into the capacitor and th value of the phasecurrent during the current flow is produced across the capacitor CK.

[0028] Another preferred variant of operation provides for one powersemiconductor of the asymmetric inverter to be closed (while the otheris open) during the off-commutation of the current from the motorwinding. This results in “soft” off-commutation; the current then eitherflows via the diode into the first series circuit or through the diodeto the other series circuit, with the off-commutation not taking placevia the main voltage source in either case.

[0029] If both the power semiconductors in the two series circuits areclosed, this results in a capacitor voltage which, as a maximum, reachesthe value of the intermediate circuit voltage. This method of operationis of secondary importance.

[0030] In one specific variant, during operation of the power converterapparatus according to the invention, one of the semiconductor switcheswhich are associated with the capacitor can be closed (the other isopen). This allows the voltage across the capacitor to be limited to adesired value, which is less than the maximum permissible voltage value.

[0031] In order to reach the maximum current amplitude quickly whencurrent flows in the motor winding, the two semiconductor switches whichare associated with the capacitor ate closed and, furthermore, the powersemiconductors which are located in the two branches of the asymmetricinverter are switched on, so that the current is forced to flow into themotor winding quickly due to the increased total voltage. Once thevoltage on the capacitor in the circuit extension has fallen to zero,the current flows through the two series circuits, which each comprise adiode and a semiconductor switch and are connected in parallel with therespective plates of the capacitor.

[0032] The operating states of the power converter apparatus accordingto the invention as described above can be combined with the normaloperating states in such a way as to approach a predetermined torqueprofile, to minimize noise, and/or to minimize or to uniformlydistribute switching losses. An operating cycle comprises forcing thecurrent to flow into the motor winding with or without an additionalvoltage from the additional voltage source, soft off-commutation onceagain with or without an additional voltage, and hard off-commutation,in each case with or without an additional voltage.

[0033] The invention covers not only the separate power converterapparatus for a reluctance motor, but also a reluctance motor havingsuch a power converter apparatus. A reluctance motor such as this with apower converter apparatus is preferably used in a vehicle with anelectrical drive, with the drive comprising one or more such reluctancemotors.

[0034] In one preferred embodiment, a connection apparatus is provided,by means of which the power converter apparatus can be connected betweenthe main voltage source and the motor winding. This connection apparatuscan also be initiated automatically, for example as a function of thespeed in a vehicle, that is to say as a function of the motor speed in avehicle which is driven by a reluctance motor. Since—as stated—thereluctance motors under discussion here have a poor torque profile atrelatively high motor speeds, the circuit extension of the powerconverter apparatus can be connected at a predetermined motor speed, inorder to achieve a torque profile which is good over the entire motorspeed range.

[0035] Exemplary embodiments of the invention will be explained in moredetail in the following text with reference to the drawing, in which;

[0036]FIG. 1 shows a schematic sketch of a switched reluctance motorwith a power converter apparatus, with the figure showing not only thenormal arrangement and configuration of a reluctance motor but also thedevelopment according to the invention;

[0037]FIG. 2 shows a sketch of a conventional power converter apparatusfor a reluctance motor of the type shown in FIG. 1;

[0038]FIG. 3 shows a schematic view of a power converter apparatusaccording to the invention, which differs from the known power converterapparatus as shown in FIG. 2 by having a circuit extension SE;

[0039]FIGS. 4 and 5 show schematic illustrations of a power converterapparatus in the “current flow” and “off-commutation” operating states;

[0040]FIG. 6 shows a schematic illustration of one specific embodimentof a power converter apparatus according to the invention; and

[0041]FIGS. 7, 8 and 9 each show, schematically, a power converterapparatus according to the invention in a given operating state.

[0042]FIG. 1 shows, schematically, a switched reluctance motor 1 with areluctance motor 2 that has three salient poles, and having a statorwhich has two stator parts S1 and S2. The rotor 2 rotates in thedirection of the arrow P corresponding to the current flow in the twostator parts S1 and S2.

[0043] The stator part S1 contains a motor winding 4 with a core 8,while the stator part S2 contains a motor winding 6 with a core 10.

[0044] The two motor windings 4 and 6 are fed from power converterapparatuses 12 and 14, respectively. The connecting nodes to the powerconverter apparatus 12 for the motor winding 4 are denoted N1 and N2.The two power converter apparatuses 11 and 12 are fed with a voltageU_(d) from a main voltage source 20 which is in the form of a DC voltageintermediate circuit here. The control device 16 controls the switchingpower semiconductors which are located in the two power converterapparatuses 11 and 14, which are identical but are driven with a timeoffset.

[0045] Only one power converter apparatus will be described in each casein the following text, as being representative of the two powerconverter apparatuses 12 and 14.

[0046]FIG. 2 shows, schematically, the design of a power converterapparatus 12 or 14 which is in the form of an asymmetric inverter. Twoseries circuits, which each comprise a switchable power semiconductor(power transistors) T1, T2 and a diode D1, D2, are connected in parallelwith the voltage U_(d) coming from the main voltage source 20.

[0047] By driving the power semiconductors T1 and T2 at the correcttime, that is to say by closing and opening the two “switches” T1 and T2at the correct time, current flows to the motor winding 4 or 6,respectively, or the current is off-commutated.

[0048]FIG. 3 shows, schematically, the idea according to the invention,namely of connecting a circuit extension SE between the motor windingand the connecting nodes N1 of the series circuit which is formed fromthe power semiconductor T1 and the diode D1. The circuit extension SEproduces an additional driving voltage for flowing to the motor winding,+U_(z) and a voltage −U_(z) which speeds up the off-commutation of thecoil current.

[0049]FIG. 4 shows, schematically, the current flow to the motor winding4 or 6. The current i_(p) which flows through the motor winding isincreased by the additional voltage U_(z), which is additivelysuperimposed on the voltage U_(d) from the main voltage source, so thatthe desired high current amplitude is reached quickly.

[0050] According to FIG. 5, the off-commutation of the coil currenti_(p) is carried out by opening the two power semiconductor switches T1and T2, as a consequence of which the current flows through the twodiodes D1 and D2. The off-commutation of the coil current is speeded upby the fact that the voltage U_(z) now has the opposite polarity to thatshown in FIG. 4.

[0051]FIG. 6 shows an embodiment for the additional voltage source whichis connected between the connecting nodes N1 between the two componentsT1 and D1 and the motor winding. Two series circuits which are connectedin parallel with one another and each comprise a diode D3 and D4,respectively, and a semiconductor switch T3 and T4, respectively, areeach connected to one plate of a capacitor CK. The connecting nodesbetween the two semiconductor switches T3 and T4, respectively, and thediodes D3 and D4, respectively, are denoted N4 and N5, respectively.

[0052] Various possible operating states of the power converterapparatus as shown in FIGS. 7 to 9 will be explained in more detail inthe following text. The various operating states include current flowingto and the off-commutation of the current for the motor windings 4 and6. In order to assist the current flow and to reach the maximum currentamplitude in the motor winding more quickly, the two semiconductorswitches T3 and T4 are closed, once the capacitor CK has been charged.In order to speed up the off-commutation of the current from the motorwinding, the two semiconductor switches T3 and T4 are opened, as isillustrated in FIG. 6.

[0053] If the two power semiconductors T1 and T2 are closed, while T3and T4 are opened, the capacitor can be charged until the current in themotor winding decreases to zero. The additional voltage is then equal tothe intermediate circuit voltage. This method of operation is ofsecondary importance in practice.

[0054] T1 or T2 is opened for “soft” off-commutation of the current inthe motor winding. In consequence, the current flows via D1 or D2. Theoff-commutation does not take place via the DC voltage intermediatecircuit. A voltage is built up across the capacitor CK. The maximumvoltage value depends on the capacitance of the capacitor, the time forwhich the current flows and the profile of the current while it isflowing. Care should be taken to ensure that the capacitor CK is chargedonly for as long as its maximum permissible voltage and the maximumpermissible voltage on the connected power semiconductor D3, D4, T3, T4are not exceeded. Alternatively, it is also possible to adapt thevoltage class and/or the capacitance of the capacitor, and/or thevoltage class of the connected power semiconductors.

[0055] “Hard” off-commutation of the current in the motor winding iscarried out by opening T1 and T2. In this state, the current flowsexclusively via the diodes, as is shown in FIG. 7 (see also FIG. 5). Theoff-commutation of the current is enhanced by the additional voltagewhich is provided by the capacitor CK. The energy flows not only intothe DC voltage intermediate circuit but also into the capacitor CK. Whatwas stated in the preceding item also applies to the voltage on thecapacitor.

[0056] The value of the voltage across the capacitor CK can be keptconstant by closing one of the two semiconductor switches (transistors)T3 and T4, as is illustrated for the semiconductor switch T4 in FIG. 8.

[0057] In order to speed up, that is to say to additionally drive, thecurrent in the motor winding as shown in the schematic illustration inFIG. 4, the two semiconductor switches T3 and T4 as well as the twopower semiconductors T1 and T2 (all the elements T1, T2, T3 and T4 maybe the same component types) are closed. The voltage across thecapacitor CK, whose connection to N4 has positive polarity owing to thepreceding charging process, is added to the voltage U_(d). When currentflows to the motor winding, the capacitor voltage across CK decreases.When the voltage is approximately zero, the current then flows from thenode N1 (FIG. 6) via the two series circuits D3, T3 and T4, D4, to thenode N3 for the respective motor winding 4 or 6.

[0058] The operating states described above with and without the use ofthe additional voltage source formed by the capacitor CK can becontrolled in the respectively desired manner by appropriately drivingthe power semiconductors T1 and T2 and the semiconductor switches T3 andT4, so as to achieve desired motor operation, that is to say for examplea specific torque profile, minimizing the amount of noise producedduring motor operation, or optimum distribution of the switching lossesbetween the individual semiconductor switches and power semiconductors.

[0059] The two semiconductor switches T3 and T4 which are associatedwith the capacitor are driven by the control device 16 as shown in FIG.1, matched to the driving of the power semiconductors T1 and T2. Thecontrol device 16 controls the semiconductor switches T3 and T4 insynchronism with the power semiconductors T1 and T2, to be precise witha phase offset for the two power converter apparatuses 12 and 14 for thereluctance motor.

[0060] A reluctance motor such as this can advantageously be used in anelectrically powered vehicle in which, for example, each driven wheelhas its own associated reluctance motor. In order to avoid adeterioration in the torque at high motor speeds, the circuit extensionSE as illustrated schematically in FIG. 3 and, as shown in FIG. 6,comprising the circuit between the nodes N1 and N3, can be connected tothe “conventional” power converter apparatus 12 or 14, as is indicatedat the top of FIG. 1 by the node N3 for the motor winding 4. Thisconnection process can be carried out manually via a connectionapparatus 40. This connection apparatus 40 can also be activatedautomatically as a function of the motor speed.

1. A power converter apparatus for one of two or more motor windings (4, 6) on a reluctance motor, comprising a semiconductor circuit arrangement in the form of an asymmetric inverter (T1, D1, T2, D2) which is fed from a main voltage source (20), in particular a DC voltage intermediate circuit, characterized in that an additional voltage source (SE; CK) with a variable polarity is connected in series with the motor winding, and in that a control device (16) is provided, which, matched to the operation of the inverter, a) provides an additional positive driving voltage from the additional voltage source (SE; CK) when current is flowing through the motor winding (4, 6); and/or b) assists the off-commutation of the current from the motor winding (4, 6) by means of an additional negative voltage from the additional voltage source (SE; CK), and c) when required, makes the additional voltage source inoperative.
 2. The power converter apparatus as claimed in claim 1, characterized in that the additional voltage source (SE; CK) produces a variable-amplitude voltage.
 3. The power converter apparatus as claimed in claim 1 or 2, characterized in that the additional voltage source is formed by an energy store (CK) which is fed from the connected motor winding (4, 6).
 4. The power converter apparatus as claimed in one of claims 1 to 3, characterized in that the additional voltage source is formed by a capacitor (CK) which is connected in series with the motor winding (4, 6) and with the main voltage source (20) by means of drivable semiconductor switches (T3, T4).
 5. The power converter apparatus as claimed in claim 4, having the following features: a) the semiconductor switch arrangement (30) of the asymmetric inverter contains two series circuits each formed by a switchable power semiconductor, for example a transistor (T1, T2), and a diode (D1, D2), which are both connected in parallel with the main voltage source (20); b) the motor winding (4, 6) and the capacitor (CK) are connected in series between the connecting nodes (N1, N2) of the elements of the two series circuits (T1, D1; T2, D2); and c) the capacitor is connected by means of the semiconductor switches (T3, T4) and the power semiconductors (T1, T2) such that energy is drawn from it, energy is stored in it, or its charge is not changed.
 6. The power converter apparatus as claimed in claim 5, characterized in that two series circuits, each comprising a diode (D3, D4) and a semiconductor switch (T3, T4), are connected to the plates of the capacitor (CK) and their connecting nodes (N1, N3) are connected to the connecting nodes (N1, N2) of one of the two series circuits (T1, D1; T2, D2) of the asymmetric inverter and, respectively, to the motor winding (4, 6).
 7. The power converter apparatus as claimed in claim 6, characterized in that both semiconductor switches (T3, T4) are open during the off-commutation of the current from the motor winding (4, 6).
 8. The power converter apparatus as claimed in claim 7, characterized in that both power semiconductor switches (T1, T2) of the asymmetric inverter are open during the off-commutation of the current from the motor winding.
 9. The power converter apparatus as claimed in claim 6, characterized in that one of the power semiconductors (T1, T2) is closed during the off-commutation of the current from the motor winding (4, 6).
 10. The power converter apparatus as claimed in claim 7, characterized in that one of the semiconductor switches which are associated with the capacitor is closed, in order that the charge on the capacitor does not change.
 11. The power converter apparatus as claimed in one of claims 6 to 9, characterized in that the semiconductor switches (T3, T4) which are associated with the capacitor are both closed.
 12. The power converter apparatus as claimed in one of claims 1 to 6, characterized in that the sequence of the operating states “current flows” with/without an additional driving voltage, “soft off-commutation” with/without an additional braking (negative-driving) voltage and “hard off-commutation” with/without additional braking (negative-driving) voltage are controlled by the control device such that a predetermined operating behavior is achieved for the motor.
 13. A reluctance motor having at least one power converter apparatus as claimed in one of claims 1 to
 12. 14. A vehicle having an electrical drive in the form of one or more reluctance motors as claimed in claim
 13. 15. The vehicle as claimed in claim 14, characterized by a connection apparatus (40), by means of which the power converter apparatus (12, 14) can be connected between the main voltage source (20) and the motor winding (4, 6).
 16. The vehicle as claimed in claim 15, characterized in that the connection apparatus (40) is operated automatically at a predetermined motor speed. 